1. Field of the Invention
This invention relates to a dry developer comprising a toner containing a particular polyalkylene and nonmagnetic inorganic fine powders and a method for forming images using a particular developer and a photosenstitive member having a hardness of at least a particular value of hardness.
2. Description of the Prior Art
In electrophotographic methods, firstly electrostatic latent images are produced by utilizing the property of photoconductor such as cadmium sulfide, polyvinylcarbazole,selenium, zinc oxide and the like. For example, electric charge is uniformly applied to a photoconductor layer followed by applying imagewise exposure thereto to form electrostatic latent images are developed with toner powders having a polarity opposite to that of the electrostatic latent images, and if desired, transferred to an image receiving sheet, and fixed. In the case of an apparatus having the transferring step, it is usual that the toner not transferred to an image receiving sheet and remaining on the photosensitive member is removed and the photosensitive member is repeatedly used.
As the method for removing the toner remaining on a photosensitive member, there may be usually used blade cleaning method, fur brush cleaning method, magnetic brush cleaning method and the like. These methods are carried out by contacting the cleaning member with the photosensitive member. In these methods, the cleaning member is pressed to the photosensitive member at an appropriate pressure so that the photosensitive member is subjected to scratch and the toner attaches fixedly to the photosensitive member while the cleaning member is used repeatedly. For example, Japanese Patent Application Laid-open No. 47345/1973 proposes that, for the purpose of avoiding the fixing of toner to a photosensitive member, both a friction decreasing material and an abradant material are added to a toner. Indeed, this proposal is effective to obviate the fixing of toner to a photosensitive member, but there still remains the following problem.
That is, when the friction decreasing material is added in an amount enough for obviating the toner fixing phenomenon, materials of low electric resistance such as paper powders, ozone addition products and the like can not be easily removed which are formed on or attached to the surface of a photosensitive member while the photosensitive member is used repeatedly, and, in particular, latent images formed on the photosensitive member are markedly deteriorated by the materials of low electric resistance under the conditions of high temperature and high humidity. In addition, the amounts of the friction decreasing material and the abradant material are so delicate that a toner of stable characteristics can be obtained with difficulty.
Further, a photosensitive member comprising an organic photoconductor has excellent characteristics, but there are disadvantages that the surface hardness is so low that the surface is subjected to damage and therefore, it is not desirable to clean strongly the surface of the photosensitive member. As a result, it is difficult in the case of the organic photoconductive photosensitive member to remove materials of low electric resistance, as contaminating materials, formed on the surface of the photosensitive member by corona discharging or the like, and paper powders and other materials of low electric resistance attached to the surface of the photosensitive member. In particular, when the above-mentioned materials remain on the photosensitive member at a high temperature and high humidity, the materials absorb moisture disadvantageously resulting in extremely low electric resistance and the formation of irregular latent images.
There have been developed various methods an apparatuses for fixing the toner images to a receiving member such as paper. The most popular method at present is a press-heating method using a heat roller which comprises bringing the toner image surface of a receiving sheet into contact with the surface of a heat roller whose surface is composed of a material having a releasing property with respect to the toner, and passing the toner image surface while contacting it with the heat roller under pressure. Since the surface of the heat roller and the toner images on the receiving sheet to which the toner images are to be fixed are brought into contact with each other under pressure according to the press-heating method, the heat efficiency upon fusing the toner images to the receiving sheet is very good resulting in a rapid fixation and thereby, this method is markedly effective for high speed electrophotographic copying machines.
However, according to the above-mentioned method, the heat roller surface contacts the toner images at a melted state under pressure so that a part of toner images adheres to and transferred to the surface of the heat roller, and then the toner images adhering to the roller surface are transferred again to a receiving sheet, so-called offset phenomenon, and thereby, the receiving sheet is made dirty.
In view of the foregoing, Japanese Patent Application Laid-open Nos. 65231/1974, 27546/1975 and 153944/1980 propose toners for heat roller fixation where polyalkylene is contained in the toner so as to prevent the offset. However, as a result of investigating various toners containing polyalkylene useful for preventing offset in heat roller fixation, it has been found that the above-mentioned problems concerning cleaning are not yet solved satisfactorily.